Copper theft alarm for grain bin systems

ABSTRACT

A copper theft alarm system is disclosed. The alarm system can be deployed on existing grain bins or other electrically powered equipment, allowing persons to receive an automated phone call, text message notification, or other desired notification when the system has sensed that a copper cable is being pulled out of a conduit. The notification can aid in potentially disrupting a thief&#39;s activity.

BACKGROUND

The present invention relates to an alarm for a grain bin system orother electrical equipment. More specifically the invention relates toan improved alarm system that senses when a cable supplying power orcontrol to a grain bin or associated equipment has been removed ortampered with and triggers an alarm or notification to a remote user.

Grain storage facilities are commonplace wherever crops are produced inthe United States and abroad. These facilities typically include one ormore storage buildings, often referred to as “grain bins,” in additionto equipment for handling and maintaining the stored grain, such asventilation fans, heaters, pumps and the like. In order to power theequipment, large diameter cables (typically made from copper) are runfrom each piece of equipment to an electrical panel located at thefacility. The cables are often run in underground conduits for ease ofinstallation and increased safety.

With the rising price of copper, theft of these power cables is becominga more prevalent problem worldwide. Since a typical grain bin systemincludes multiple long cable runs, each comprising heavy gauge copperwire conductors, their value on the scrap market makes them anattractive target for burglars. Additionally, because grain bins aretypically located in rural areas, theft can take place out in the openwith little probability anyone will ever witness the crime. Replacementcosts for burglarized cables can reach into the thousands or tens ofthousands of dollars including labor.

The steps required to steal a cable from a grain bin can be quite timeconsuming. First, the electrical panel must be opened to de-energize thecables. Then the ends of the cable must be disconnected from theirtermination points. Once the ends are free, the thieves will often pullthe cable out of the conduit using a chain or rope tied to a vehicle, assubstantial pulling force is often required. Since separate conduits arenormally run to each piece of powered equipment, the process must berepeated multiple times to steal all of the cables at the facility. Whatis needed is a system for notifying a remote user or otherwisetriggering a notification when a burglar has initiated the process sothat he/she may be deterred and/or caught before all of the cables havebeen removed.

Prior attempts to address grain bin cable theft have suffered fromsignificant drawbacks. For example, surveillance cameras have been usedto monitor the areas around the grain bin. However, would requireprohibitively expensive constant monitoring by personnel to detect whenthieves are present. Other devices require a dedicated external sourceto power the alarm, which increases cost and allows thieves to disablethe alarm by disconnecting the external power source. The presentinvention seeks to address at least these problems in addition toothers.

SUMMARY OF THE INVENTION

The present disclosure relates to one or more of the following features,elements or combinations thereof. A cable alarm system is disclosed. Thecable alarm system can be deployed on new or existing grain bin systemsor other electrically powered equipment.

In the illustrative embodiment, a device is deployed at the grain binwhich enables persons to receive an automated phone call, text messagenotification, or other desired notification when the system senses thata power cable supplying power to the grain bin is being pulled out of aconduit. The device and generated notification can aid in discouragingand/or disrupting the thief's activity while potentially allowing forintercepting the valuable copper power cable.

Additional features of the disclosure will become apparent to thoseskilled in the art upon consideration of the following detaileddescription of preferred embodiments exemplifying the best mode ofcarrying out the invention as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overview of a grain bin system according to one embodimentof the invention.

FIG. 2 is a diagrammatic view of a cable theft alarm according to oneembodiment which is suitable for installation with a grain bin system,such as that of FIG. 1.

FIG. 3 is a circuit diagram of an illustrative control circuit for acable theft alarm according to one embodiment which is suitable forinstallation in a grain bin system, such as that shown in FIG. 1.

FIG. 4 is another circuit diagram of a second illustrative controlcircuit for a cable theft alarm according to another embodiment which issimilarly suitable for installation in a grain bin system, such as thatshown in FIG. 1.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described embodiments, and any further applications of theprinciples of the invention as described herein are contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

Disclosed is an alarm for a grain bin system or other electricallypowered equipment. The device operates in connection to a grain binsystem to detect an attempted theft and, as a result, provides anotification to a designated user. In one form, the device is capable ofproviding this notification in the form of a phone call (such as to apredetermined number), a text message (SMS or the like), an e-mail, adata packet (such as at least one UDP datagram or TCP packet), or someother suitable method of notification.

Turning to FIG. 1, a perspective view of a grain bin system 10 accordingto one embodiment of the present disclosure is shown. As shown in FIG.1, an exemplary grain bin system 10 includes one or more storage bins 12with various associated equipment, such as ventilation fans 16,connected thereto. Other equipment for moving or maintaining grain maybe provided with the grain bin system 10 including pumps, heaters,augers, conveyors, and the like. Electrical panel 14 provides power froman external source 15 to the equipment via cables 18 which are installedin conduits 19. Electrical panel 14 may also control, for example, anumber of aspects of grain bin system 10, including the activation andspeed of the fans 16 and the operation of other drying orloading/unloading equipment associated with the bins 12.

Cables 18, depending on the types of equipment being controlled orsupplied, are often composed of multi-conductor cables, includingcopper, protected by an outer weatherproof and shielded housing. Due totheir size and quantity, cables 18 are viewed by would-be burglarsinterested in vandalizing and removing them as a significant source ofcopper wire which can be sold for a significant sum of money as scrapmetal.

Turning to FIG. 2, with continued reference to FIG. 1, according to oneembodiment of the present disclosure, a telemetry box 22 is provided foruse with grain bin system 10. Telemetry box 22 may provide formonitoring of the details, such as air flow, temperature, humidity,equipment position or state, etc., or to report when the grain bin orassociated equipment fails. Telemetry box 22 and/or control panel 14 mayalso include communication equipment suitable for providing remoteaccess, monitoring, and/or control of grain bin system 10. Telemetry box22 may be mounted, for example, adjacent or near the electrical panel14, as shown in FIG. 1.

Telemetry box 22 may include or be coupled to alarm circuit 24, as shownherein, such that it monitors the electrical continuity of a conductivesensing loop 20. Telemetry box 22 also preferably provides aweatherproof environment for alarm circuit 24. In one form, the sensingloop 20 is inserted into the conduits 19 in a serial fashion as shown,with the ends 30 and 32 of the loop 20 connected to the alarm circuit24. The conductors of the sensing loop 20 are preferably insulated andsized to be smaller than the cables 18 in order to allow fitment intothe conduits 19 with the larger cable 18 being protected. For example,the cable(s) of the sensing loop 20 may be 10, 12, 14, 16, 18, 20 or 22gauge wire. In one form, portions of the sensing loop are formed byrunning two conductors through the entire length of one of the conduits19 alongside the power cable 18 and connecting first ends of theconductors at an end of the conduit. The other ends of the conductorsare then serially connected to the sensing loop 20 or directly to thealarm circuit 24. In another form, portions of the sensing loop may bepartially inserted into the conduits 19 up to a length needed tofacilitate breakage of the loop when cable 18 is pulled out of theconduit.

Due to the tight clearance typically found between the cables 18 and theinner walls of the conduits 19, if a burglar attempts to pull any one ofthe cables 18 from a conduit 19, the resulting force will break thecorresponding portion of the sensing loop 20, causing an open circuitcondition. This will activate radio transmitter 26 to deliver anotification of a selected type to a pre-determined user and/ordestination.

Alarm circuit 24 is preferably programmed such that after a successfulnotification(s) has been delivered by radio transmitter 26, the radiotransmitter 26 is automatically deactivated. Furthermore, when cable 18and sensing loop 20 are repaired, replaced, or otherwise restored, andsubsequently re-connected, alarm circuit 24 automatically arms andcontinues monitoring the continuity of sensing loop 20.

Electrical panel 14 may optionally include a door sensor 25 whichindicates whether a door of the panel 14 is open or closed. According toone form, the door sensor comprises a limit switch having a contact 34that is closed when the panel door is closed and open when the paneldoor is open. The sensing loop 20 is connected through the door sensor25 as shown, such that the continuity of the sensing loop 20 ismaintained when the panel 14 is closed. However, when the panel 14 isopened, the continuity of sensing loop 20 will be interrupted.

In order to prevent false alarm notifications from being sent when thepanel 14 is opened for service or other authorized activity, a keysensor 27 may be optionally provided. The key sensor 27 preferablycomprises a contact 36 which is operatively connected to the panel keylock 29 and wired in parallel with the door sensor 25 as shown. When akey is properly inserted into the lock, the contact 36 will close,thereby maintaining continuity in the sensing loop 20 when the panel 14is opened for service. However, if the panel 14 is opened without theusing the key (such as during an attempted theft), both of the contacts34 and 36 will be open, which will interrupt the continuity of thesensing loop 20 and trigger an alarm notification. Since thieves willtypically break open electrical panels to disconnect power to the targetcables before beginning the removal process, this provides an earlywarning to the property owner and/or law enforcement that an attemptedtheft is about to take place.

According to one form radio transmitter 26 (or 126 as described later)is a cellular communication device, such as a cellular radio, operatingon a known cellular network, such as the GSM, LTE or CDMA wirelessnetworks operated by AT&T or Verizon Wireless, or the like. It shall beappreciated that the cellular communication device may be programmed totransmit a notification signal in either a voice or data formatdepending upon user preference or any other factor.

It shall be appreciated that one or more of the components of alarmcircuit 24 may be included as a portion of a printed circuit boardserving a separate or related purpose within telemetry box 22.Alternatively, telemetry box 22 may be dedicated specifically to alarmcircuit 24.

According to the embodiment illustrated in FIG. 2, alarm circuit 24 ispowered by an internal battery 28. Suitable batteries for use asinternal battery 28 are one or more XL-050F ½ AA 3.6V Lithium batteriessold by Xeno Energy USA located in Watertown, Conn. In a further form,the alarm circuit 24 operates automatically whenever grain bin system 10is not operating (e.g., when fan 16 is turned off). Operation of thegrain bin system is detected by a voltage within cable 18 or the like.Preferably, battery 28 is of sufficient capacity to supply power to thealarm circuit 24 for five years or more under constant monitoring usewithout requiring replacement. Additionally, battery 28 is preferablyon-board in that it is housed within, on, or proximate to telemetry box22, which contains alarm circuit 24.

During installation, conductors 30 and 32, which form portions ofsensing loop 20, are connected to terminals on the alarm circuit 24,which may also be terminals of telemetry box 22. Given the abovedescribed connection, in the event a cable 18 is pulled from its conduit(thereby breaking a conductor in the sensing loop 20) or electricalpanel 14 is opened without the key, electrical continuity through thesensing loop 20 will be lost. This triggers alarm circuit 24 to turn onradio transmitter 26 and relay the predetermined theft notifications.Below, a description of how this condition is detected and handled byalarm circuit 24 will be described in more detail.

Alarm circuit 24 is designed to handle two states: “Alarm ON and ARMED”and “Alarm ON and TRIGGERED”. According to this embodiment, battery 28is comprised of four (4) 3.6 volt lithium batteries connected in seriesto supply positive (+) 13.8 volts through diode 40 to alarm circuit 24.When the alarm switch 42 is closed, current flows through resistor 44and charges capacitor 46. Current also flows through resistors 48 and 50out into conductor 30, which is connected to terminal 52. If theconductivity path in the sensing loop 20 is unbroken the current returnsto the GND terminal screw 54 on the alarm circuit 24 (which may also beconnected to an external connection of telemetry box 22). Resistor 56completes the circuit back to the negative side of battery 28. In theillustrated form, the ratio of resistor 48 (4.7 megohm) to that ofresistor 50 and resistor 56 is 42:1. Thus, when sensing loop 20 isunbroken, the base of transistor 60 is held low, such that transistor 60is not conducting and no current flows from collector to emitter undernormal circumstances.

When the illustrative alarm circuit 24 is armed, silicon controlledrectifier (SCR) 62 is not conducting. The optocoupler IC3 64 is also notconducting in this state. Resistor 66 holds the base of transistor 68low. Again, in the ARMED state transistor 68 is not conducting and nocurrent flows from collector to emitter, and as such radio transmitter26 is off.

Alarm circuit 24 transitions from the ARMED to the TRIGGERED state whenthe circuit connection between conductor 30 and conductor 32 is opened(i.e. when sensing loop 20 is broken due to removal of a cable 18 or theelectrical panel 14 is opened without the key). As a result, the voltageat the base of transistor 60 rises. Accordingly, transistor 60 turns onand saturates. Capacitor 46 discharges through transistor 60 andresistor 70. A voltage appears at the gate of SCR 62. This voltage issufficient to trigger the SCR 62 into conduction. As a result, currentflows from battery 28 through resistor 72 and through anode to thecathode of SCR 62. The current through SCR 62 is sufficient to latch theSCR into conduction. The voltage at the base of transistor 68 rises toapproximately ⅔ of the supply voltage due to the resistance ratiobetween resistors 66 and 72 causing transistor 68 to turn on. Transistor68 begins conducting from collector to emitter which turns on radiotransmitter 26. Radio transmitted 26 is configured to transmit anotification to a predetermined user/destination via a selected formatupon activation.

After the notification has been transmitted by radio transmitter 26,software commands within the radio transmitter turn on transistor 74(GPIO-3). This enables current to flow from the battery 28 throughresistor 76 and through the input side (LED) of optocoupler IC3 64. Thiscauses the phototransistor output of IC3 64 to turn on and current toflow from collector to emitter. The output current of IC3 64 shunts outthe anode and cathode of SCR 62. The current through SCR 62 falls belowthe holding current and SCR 62 turns off. The current flowing throughIC3 64 maintains the voltage at the base of transistor 68 and IC3 64continues to hold transistor 68 on.

After 3 seconds transistor 74 (GPIO-3) turns off. IC3 64 resultantlyturns off. Resistor 66 pulls the base of transistor 68 low. Transistor68 turns off which turns off the radio transmitter 26. After thetriggering of an alarm, alarm circuit 24 remains in the TRIGGERED stateuntil the sensing loop 20 is repaired and continuity is re-establishedbetween conductor 30 and conductor 32, at which point the circuitautomatically resets to the ARMED state.

Capacitor 78 is used to slow the rise of voltage at the base oftransistor 60. This reduces the possibility of false triggering fromtransient voltages on the sensing loop conductors. Metal oxide varistor80 and resistors 50 and 56 protect the alarm circuit from lightning andother transient voltages that may develop in the sensing loop 20.

Turning to FIG. 3, with continued reference to FIG. 1, according toanother embodiment of the present invention, alarm circuit 124 may beused in conjunction with telemetry box 22 and the other components ofFIG. 1 as described above with respect to alarm circuit 24. It shall beappreciated that one or more of the components of alarm circuit 124 maybe included on a portion of a printed circuit board within telemetry box22, or alarm circuit 124 may be contained within telemetry box 22 as astand alone board. According to the embodiment illustrated in FIG. 3,alarm circuit 124 is powered by an internal battery 128. In a furtherform, the alarm circuit 124 operates automatically whenever grain binsystem 10 is not operating (e.g., fans 16 or other equipment are notrunning) Preferably, battery 128 is of sufficient capacity to supplypower to the alarm circuit 124 for five years or more without requiringreplacement. Additionally, battery 28 is preferably on-board in that itis housed within or proximate to telemetry box 22.

During installation, conductor 30, which forms a connection point tosensing loop 20, is connected to a terminal 152 on the alarm circuit 124of telemetry box 22. A grounding screw inside telemetry box 22physically connects the circuit board GND terminal 154 to a metalstructure of grain bin system 10 or other suitable ground. Conductor 32,which forms a return path from sensing loop 20, is also connected to theGND terminal 153. The sensing loop 20 (via conductors 30, 32, and otherconductors in the sensing loop 20) completes the external circuit foralarm circuit 124.

Given the above described connection, in the event a cable 18 is pulledfrom its conduit (thereby breaking a conductor in the sensing loop 20)or electrical panel 14 is opened without the key, electrical continuitythrough the sensing loop 20 will be lost. This triggers alarm circuit124 to turn on radio transmitter 126 and relay theft notifications.Below, a description of this condition is detected and handled by alarmcircuit 124 will be described in more detail.

Alarm circuit 124 is designed to handle two states: “Alarm ON and ARMED”and “Alarm ON and TRIGGERED”. According to this embodiment, battery 128is comprised of four (4) 3.6 volt lithium batteries connected in seriesto supply positive (+) 13.8 volts to alarm circuit 124. Current flowsthrough resistors 127 and 128 and out into the conductor 30 of sensingloop 20 via terminal 152. If the conductivity path in the sensing loop20 is unbroken the current returns to the GND terminal 154. Oncereceived at the GND terminal 154, the circuit is completed via resistor130 to the negative side of battery 128. In the illustrated form, theratio of resistor 127 (1 megohm) to that of resistor 128 (15 kilohm) andresistor 130 (15 kilohm) is 33:1. This holds the base of transistor 132low. Thus, in this state, transistor 132 is not conducting and nocurrent flows from collector to emitter under normal circumstances.

Furthermore, when the alarm circuit 124 is in the Alarm ON and ARMEDstate, capacitor 135 has equal potential (13.8 v) on both plates. As aresult, the output of IC 134 is held low and resultantly, the base oftransistor 136 is held low through resistor 138. In this state,transistor 136 will not conduct and therefore, radio transmitter 126 ispowered off.

Alarm Circuit 124 is triggered when the circuit connection betweenconductor 30 and conductor 32 is opened (i.e. when sensing loop 20 isbroken due to removal of a cable 18 or the electrical panel 14 is openedwithout the key). As a result, the voltage at the base of transistor 132rises. Accordingly, transistor 132 turns on and saturates. One plate ofcapacitor 135 is pulled low through transistor 132. Resultantly, anegative pulse appears at input pins 138 and 140 of IC 134. This causesa positive pulse at output 142 of IC 134, given its NOR logic. Theflip-flop circuit of IC 134 is activated and output pin 144 goes high.As a result, the base of transistor 136 is pulled high and causestransistor 136 to turn on. Transistor 136 begins conducting fromcollector to emitter and turns on radio transmitter 126.

After a preselected message has been transmitted by radio transmitter26, software commands within the radio transmitter turn on transistor174 (OUT 1). Pin 146 is pulled low through diode 148. This deactivatesthe flip-flop circuit in IC 134 and pin 144 resultantly goes low.Accordingly, the base of transistor 136 goes low and transistor 136stops conducting, thereby turning off radio transmitter 126. The alarmcircuit remains in this state until the sensing loop 20 is repaired andcontinuity is re-established between conductor 30 and conductor 32. Whenthe continuity of sensing loop 20 is re-established, the alarm circuitautomatically re-arms.

Capacitor 178 is used to slow the rise of voltage at the base oftransistor 132. This reduces the possibility of false triggering fromtransient voltages in the sensing loop 20 by introducing a short timedelay, such as 1-2 seconds, before triggering. The TVS diode 180protects the alarm circuit from lightning and other transient voltagesthat may develop in the sensing loop 20. These transients can occur whenelectrical components in the grain bin system fail.

Resistor 182 and capacitor 184 are used to soft-start the circuit andprevent false alarms when the battery 128 is first installed orreplaced. Capacitor 186 prevents EMI and RFI signals from triggering thedevice. Resistors 188 and 190 maintain an equal charge on the plates ofcapacitor 135 when the alarm circuit 124 is armed. Resistors 192 and 194limit the current into the radio transmitter 126, while diodes 148 and149 provide reverse polarity protection for radio transmitter 126.

The disclosed circuit design allows for universal compatibility with allbrands of grain bin systems and equipment. It is independent of theconductors that supply power to the grain bin and works seamlessly withnormal operation of the associated equipment. In the illustratedembodiment, the disclosed circuit design draws only 0.000035 Amperes (35micro-amperes) utilizing a potential of 13.8 DC volts, allowingbattery-life to last at least 3 years without recharge or replacement.Preferably, other designs would draw less than 100 micro-amperes when inthe armed state (i.e. not during a triggered state when the radiotransmitter is in operation.) Other alarm solutions utilize highervoltage solutions which require additional external batteries, solarpanels, generators, or utility power to maintain current within thesensing loop conductors. Such designs pose reliability and safety risks,as well as introducing inefficient energy consumption. The disclosedcircuit design manages power more efficiently and eliminates the needsfor external power supplies which can deter from the reliability of thealarm system. For example, several consecutive cloudy days can cause asolar powered system to lose its charge, thereby generating a falsealert or render the alarm system ineffective.

The disclosed system may also be used to prevent copper cable theft forother types of electrically powered equipment located in remote areas,such as agricultural well pumps, construction trailers, or backupgenerator installations.

While the disclosure is susceptible to various modifications andalternative forms, specific exemplary embodiments thereof have beenshown by way of example in the drawings and have herein been describedin detail. It should be understood, however, that there is no intent tolimit the disclosure to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the disclosure asdefined by the appended claims.

A plurality of advantages arises from the various features of thepresent disclosure. It will be noted that alternative embodiments ofvarious components of the disclosure may not include all of the featuresdescribed yet still benefit from at least some of the advantages of suchfeatures. Those of ordinary skill in the art may readily devise theirown implementations of an alarm system that incorporate one or more ofthe features of the present disclosure and fall within the spirit andscope of the disclosure.

What is claimed is:
 1. An anti-theft system for an electric power cablecomprising: a radio transmitter for generating a notification to apredetermined recipient; and a conductive sensing loop having first andsecond ends, said sensing loop installed in at least one conduit withthe power cable, wherein at least one portion of the sensing loop isformed by running two conductors through a conduit alongside the powercable and connecting first ends of the conductors at a first end of theconduit; an alarm circuit coupled to said radio transmitter, said alarmcircuit comprising: a first circuit for supplying a continuous voltageto said first end of said conductive sensing loop; and a second circuitfor detecting said continuous voltage at said second end of saidconductive sensing loop and triggering said notification by providingpower to said radio transmitter when said continuous voltage isdisrupted.
 2. The anti-theft system of claim 1, wherein the conductivesensing loop comprises an electrical conductor sized to facilitatebreakage of the conductor when the power cable is pulled out of theconduit.
 3. The anti-theft system of claim 1, wherein the conductivesensing loop comprises an electrical conductor having a smaller diameterthan said electric power cable.
 4. The anti-theft system of claim 1,wherein the conductive sensing loop comprises a plurality of conductorsegments connected in series, said conductor segments forming anelectrically continuous path between said first and second ends.
 5. Theanti-theft device of claim 1, wherein said conductive sensing loop isinstalled in a plurality of conduits containing power cables.
 6. Theanti-theft system of claim 1, further comprising: an on-board battery,the battery supplying at least a portion of said continuous voltage. 7.The anti-theft device of claim 1, wherein no external power source isused in providing said continuous voltage.
 8. The anti-theft system ofclaim 1, further comprising a door sensor wired serially within saidsensing loop, said door sensor configured to disrupt said continuousvoltage when a door of an access panel associated with the power cableis opened.
 9. The anti-theft system of claim 8, wherein said door sensorcomprises a limit switch.
 10. The anti-theft system of claim 8, furthercomprising a key sensor wired in parallel with the door sensor, the keysensor configured to maintain said continuous voltage when the door isopened using a key.
 11. The anti-theft device of claim 1, wherein saidradio transmitter is a cellular radio.
 12. The anti-theft device ofclaim 11, wherein said notification is a telephone call.
 13. Theanti-theft device of claim 11, wherein said notification is a textmessage.
 14. The anti-theft device of claim 1, wherein said power cableis connected to a grain bin system.
 15. The anti-theft device of claim14, wherein said power cable is connected to a fan motor of the grainbin system.
 16. The anti-theft system of claim 1, wherein said powercable is connected to a water well pump.
 17. A method for detecting anattempted theft of at least one electric power cable, comprising:installing a conductive sensing loop into a plurality of conduitscontaining power cables such that the conductive sensing loop will bebroken when any one of the power cables is pulled out of the conduit,wherein at least one portion of the sensing loop is formed by runningtwo conductors through the plurality of conduits alongside the powercables and connecting first ends of the conductors at a first end of oneof the plurality of conduits; connecting a first and second end of thesensing loop to an alarm circuit; supplying a continuous voltage fromthe alarm circuit to the first end of the sensing loop; detecting thatthe continuous voltage is not present at the second end of the sensingloop; and triggering a notification, based on said detecting, to apredetermined recipient by providing power to a radio transmitterconnected to the alarm circuit.